Tuned transition from quantum to classical for macroscopic quantum states

TL;DR

This study demonstrates a tunable flux qubit system that exhibits a controlled transition from quantum to classical behavior by adjusting the tunnel barrier, revealing insights into the quantum-classical boundary.

Contribution

It introduces a method to tune a flux qubit from quantum to classical regimes, showing how macroscopic quantum states can be manipulated and observed.

Findings

Increased state lifetime at high barriers

Observation of spontaneous coherent oscillations

Transition from quantum to classical behavior achieved

Abstract

The boundary between the classical and quantum worlds has been intensely studied. It remains fascinating to explore how far the quantum concept can reach with use of specially fabricated elements. Here we employ a tunable flux qubit with basis states having persistent currents of 1$ \mu$A carried by a billion electrons. By tuning the tunnel barrier between these states we see a cross-over from quantum to classical. Released from non-equilibrium, the system exhibits spontaneous coherent oscillations. For high barriers the lifetime of the states increases dramatically while the tunneling period approaches the phase coherence time and the classical regime is reached.